Process for producing a magnetic recording material

Abstract

A process for producing a magnetic recording medium is described in which a hardening agent and a lubricant are added to a magnetic coating solution prior to coating thereof on a non-magnetic support. It has been found that improved magnetic recording properties and consistent product characteristics are obtained if the addition of the hardening agent and lubricant to the magnetic coating solution is carried out within about 240 minutes of surface calendering treatment of the magnetic recording medium.

What is claimed is: 
     
       1. A process for producing a magnetic recording medium comprising the steps of: (i) kneading a ferromagnetic powder in a binder solution, wherein said powder is dispersed into said binder solution, so as to form a magnetic coating dispersion;   (ii) adding a hardening agent and a fatty acid to said dispersion formed in step (i) so as to form a magnetic coating composition;   (iii) coating the magnetic coating composition formed in step (ii) on a non-magnetic support; and   (iv) carrying out a calendering treatment of the coated support formed in step (iii), wherein the calendering treatment is carried out at a linear pressure of 80 to 500 kg/cm with a calender roll temperature of 50° to 150° C. and the calendering treatment is completed within 240 minutes after addition of the hardening agent or the fatty acid to the dispersion, whichever is added first.   
     
     
       2. The process of claim 1, wherein after the calendering treatment, the magnetic recording medium is dried so that the coated film has a residual solvent content of 0.1 weight % or less. 
     
     
       3. The process of claim 1, wherein the binder is a thermoplastic resin, a thermosetting resin, a reactive resin or a mixture of at least two thereof. 
     
     
       4. The process of claim 1, wherein the hardening agent is a hardenable component or a hardening reaction catalyst. 
     
     
       5. The process of claim 1, wherein the hardenable component is a compound or resin having at least one isocyanate group in its molecule. 
     
     
       6. The process of claim 1, wherein the hardening reaction catalyst is an amine, an organometallic compound, an alkali metal compound or a radical generator. 
     
     
       7. The process of claim 1, wherein the hardening agent and the fatty acid are added together to the dispersion of ferromagnetic particles and binder. 
     
     
       8. The process of claim 1, wherein the hardening agent and the fatty acid are added sequentially to the dispersion of ferromagnetic particles and binder. 
     
     
       9. The process of claim 1, wherein prior to calendering the coated magnetic layer is dried to a residual solvent content of from 0.3 to 3 weight %.